diff options
| author | Tom Rini <trini@ti.com> | 2013-03-18 12:31:00 -0400 |
|---|---|---|
| committer | Tom Rini <trini@ti.com> | 2013-03-18 14:37:18 -0400 |
| commit | 0ce033d2582129243aca10d3072a221386bbba44 (patch) | |
| tree | 6e50a3f4eed22007549dc740d0fa647a6c8cec5b /doc/README.displaying-bmps | |
| parent | b5bec88434adb52413f1bc33fa63d7642cb8fd35 (diff) | |
| parent | b27673ccbd3d5435319b5c09c3e7061f559f925d (diff) | |
Merge branch 'master' of git://git.denx.de/u-boot-arm
Albert's rework of the linker scripts conflicted with Simon's making
everyone use __bss_end. We also had a minor conflict over
README.scrapyard being added to in mainline and enhanced in
u-boot-arm/master with proper formatting.
Conflicts:
arch/arm/cpu/ixp/u-boot.lds
arch/arm/cpu/u-boot.lds
arch/arm/lib/Makefile
board/actux1/u-boot.lds
board/actux2/u-boot.lds
board/actux3/u-boot.lds
board/dvlhost/u-boot.lds
board/freescale/mx31ads/u-boot.lds
doc/README.scrapyard
include/configs/tegra-common.h
Build tested for all of ARM and run-time tested on am335x_evm.
Signed-off-by: Tom Rini <trini@ti.com>
Diffstat (limited to 'doc/README.displaying-bmps')
| -rw-r--r-- | doc/README.displaying-bmps | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/doc/README.displaying-bmps b/doc/README.displaying-bmps new file mode 100644 index 00000000000..331154166d9 --- /dev/null +++ b/doc/README.displaying-bmps @@ -0,0 +1,27 @@ +If you are experiencing hangups/data-aborts when trying to display a BMP image, +the following might be relevant to your situation... + +Some architectures cannot handle unaligned memory accesses, and an attempt to +perform one will lead to a data abort. On such architectures it is necessary to +make sure all data is properly aligned, and in many situations simply choosing +a 32 bit aligned address is enough to ensure proper alignment. This is not +always the case when dealing with data that has an internal layout such as a +BMP image: + +BMP images have a header that starts with 2 byte-size fields followed by mostly +32 bit fields. The packed struct that represents this header can be seen below: + +typedef struct bmp_header { + /* Header */ + char signature[2]; + __u32 file_size; + __u32 reserved; + __u32 data_offset; + ... etc +} __attribute__ ((packed)) bmp_header_t; + +When placed in an aligned address such as 0x80a00000, char signature offsets +the __u32 fields into unaligned addresses (in our example 0x80a00002, +0x80a00006, and so on...). When these fields are accessed by U-Boot, a 32 bit +access is generated at a non-32-bit-aligned address, causing a data abort. +The proper alignment for BMP images is therefore: 32-bit-aligned-address + 2. |